The present invention relates to a novel piperazine derivative having pharmacological activity, to processes for its preparation, to compositions containing it, and to its use in the treatment of neurological or psychiatric disorders such as cognitive impairment e.g. in Alzheimer's disease.
The histamine H3 receptor is predominantly expressed in the mammalian central nervous system (CNS), with minimal expression in peripheral tissues except on some sympathetic nerves (Leurs et al., (1998), Trends Pharmacol. Sci. 19, 177-183). Activation of H3 receptors by selective agonists or histamine results in the inhibition of neurotransmitter release from a variety of different nerve populations, including histaminergic and cholinergic neurons (Schlicker et al., (1994), Fundam. Clin. Pharmacol. 8, 128-137). Additionally, in vitro and in vivo studies have shown that H3 antagonists can facilitate neurotransmitter release in brain areas such as the cerebral cortex and hippocampus, relevant to cognition (Onodera et al., (1998), In: The Histamine H3 receptor, ed. Leurs and Timmerman, pp 255-267, Elsevier Science B.V.). Moreover, a number of reports in the literature have demonstrated the cognitive enhancing properties of H3 antagonists (e.g. thioperamide, clobenpropit, ciproxifan and GT-2331) in rodent models including the five choice task, object recognition, elevated plus maze, acquisition of novel task and passive avoidance (Giovanni et al., (1999), Behay. Brain Res. 104, 147-155). The histamine H3 receptor antagonist GSK189254 inhibited [3]R-α-methylhistamine ex vivo binding in the rat cortex following oral administration to the rat, and at certain oral doses improved performance of rats in the following cognition paradigms: passive avoidance, water maze, object recognition, and attentional set shift (A. D. Medhurst et al., J. Pharmacol. Exp. Therap., 2007, 321(3), 1032-1045.).
These data suggest that novel H3 antagonists and/or inverse agonists could be useful for the treatment of cognitive impairments in neurological diseases such as Alzheimer's disease or a related neurodegenerative disorder.
WO 2005/040144 A1 (Glaxo Group Limited) discloses a series of 1-benzoyl-substituted diazepanyl derivatives having affinity for and being antagonists and/or inverse agonists of the histamine H3 receptor. Example 10 of WO 2005/040144 A1 discloses 1-(isopropyl)-4-{[4-(tetrahydro-2H-pyran-4-yloxy)phenyl]carbonyl}hexahydro-1H-1,4-diazepine hydrochloride:

WO 2004/037801 A1 (Janssen Pharmaceutica, N.V.) discloses a series of piperazinyl and diazepanyl benzamides and benzothiamides with the ability to modulate the activity of the histamine receptor, specifically the H3 receptor.
WO 2004/101546 A1 (Glaxo Group Limited) discloses a number of (piperidine-4-carbonyl)-piperazine derivatives and (piperidine-4-carbonyl)-[1,4]-diazepane derivatives having affinity for and being antagonists and/or inverse agonists of the histamine H3 receptor.
WO 03/004480 A2 (Novo Nordisk A/S and Boehringer Ingelheim International GmbH) discloses a series of substituted piperazines and diazapanes having binding affinity to the histamine H3 receptor.